Air seeders and other seeding devices are commonly towed by tractors to apply seed or fertilizer, or both simultaneously, to a field. As an example, an air seeder may be towed in combination with a tilling implement, one behind the other, to place seed and fertilizer under the surface of the soil. An air seeder has as its central component a wheeled seed cart which comprises one or more frame-mounted product tanks for holding product, generally seed or fertilizer or both. Air seeders also generally include a metering system for dispensing product from the tanks and a pneumatic distribution system for delivering the product from tank to soil.
An air seeder may include product tanks which are pressurized with air from the pneumatic distribution system. The pneumatic distribution system of an air seeder generally utilizes a centrifugal fan to provide at least one airstream which flows through the pneumatic distribution system to seed boots where product is deposited in the soil. Product is first introduced to the air stream by the metering system at a venturi in the primary distribution manifold located below the metering system. Product is carried by the air stream through distribution lines to a series of secondary distribution manifolds (“headers”), which in turn distribute product through distribution lines to seed boots mounted behind ground openers on the tilling implement so that the product may be evenly delivered to the span of ground acted upon by the tilling implement.
In positive pressure seeding systems, some air is diverted from the pneumatic distribution system to the product tanks to pressurize the tanks. Ideally, the product tanks are maintained at the same pressure as the airstream which carries product from the product tank. If air pressure in the product tanks is too low the product will not enter the airstream correctly and pulsing will occur. If air pressure is too high, “blow-by” of unmetered product by the bottom or top of the meter will occur. Either of these situations is undesirable.
With air seeders as described above, it is not currently possible to automatically control seed population on a row by row basis, particularly in the event that it is desirable to seed with certain rows while not seeding with other rows. With other types of row crop planters using individually driven seed meters at the row unit, such as corn or soybean planters on a 30 inch row spacing, it is known to independently drive the seed meters such that each row can plant at different seed populations, or not seed at all. However, with an air seeder, the metering is typically done in more of a bulk manner at the primary distribution manifold, and the seeds are then further directed toward the different row units at the secondary headers. Examples of primary and secondary distribution manifolds which may be used with air seeders are disclosed in U.S. Pat. No. 5,947,040 (Gregor) and U.S. Pat. No. 5,980,163 (Gregor et al.), each of which are assigned to the assignee of the present invention and incorporated herein by reference.
What is needed in the art is an air seeder which allows product application independently on a row by row basis, subject to current operating parameters.